Our broad aim is to better understand the molecular basis for the biological roles of lactoferrin, the major iron-binding protein in milk, other bodily secretion and leukocytes. This will have important implications for other transferrins and for binding proteins generally. The research will address the binding and release of metal ions and anions by lactoferrin, and will implications for understanding the control of iron levels in biological fluids, bodily defence mechanisms (especially anti- bacterial activity), aspects of the biology of human milk and the bioavailability of trace elements. It will build on the recent solution of the structure of human iron-lactoferrin, Fe2 Lf,through X-ray crystallographic analyses of other structural forms of lactoferrin comparisons with related proteins, and complementary spectroscopic and biochemical studies. Specific aims are: (I) Completion of the crystallographic refinement of the human Fe2 Lf, structures at 2.2 A resolution. (II) High resolution X-ray structure analyses of human apo-lactoferrin, form two new crystal forms recently obtained. These are aimed at defining the conformational changes accompanying iron binding and release. (III) Investigation of the structural effects (if any) of glycosylation through comparative structural studies of native and deglycosylated forms of lactoferrin. (IV) Crystallization and structure analyses of other forms of lactoferrin, including monoferric lactoferrin, and fragments of lactoferrin. (V) Crystallographic and spectroscopic comparisons of lactoferrin with other metals and anions substituted, including refinement of the structure of copperlactoferrin. (VI) Structural comparisons with other transferrins and with bacterial binding proteins, in particular the SO4 2- binding protein from Salmonella typhimurium. (VII) Crystallization of related proteins especially melanotransferrin and bovine lactoferrin, for subsequent structure analyses. (VIII) As a long-term aim, crystallographic studies on site-specific mutants of lactoferrin.